1. Field of the Invention
The present invention relates to an ultrasonic transducer for measuring the propagation delay time and the like by propagating ultrasonic waves to an object to be measured.
2. Description of the Related Art
In general, ultrasonic measuring instruments, such as ultrasonic rangefinders and ultrasonic flowmeters, are so arranged as to output ultrasonic waves of a predetermined frequency from an ultrasonic transducer., detect reflected or transmitted waves thereof, convert the same into an electrical signal, and calculate the propagation delay time and the like on the basis of the received signal detected. As for this propagation delay time, a time interval between the time of transmission and the time of reception of a pulse is conventionally determined by the count of clock pulses included in that time interval. Accordingly, a time duration shorter than that corresponding to one clock pulse is ignored, with the result that a quantization error has conventionally occurred by that portion of time.
As a means for overcoming the above-described problem, Japanese Patent Application Laid Open No. 225027/1985 discloses an apparatus in which the time duration shorter than that corresponding to one clock pulse is determined by integrating a time duration from the time of transmission of a pulse to the rise of a clock pulse and a time duration from the time of reception of the pulse to the rise of a clock pulse by means of an integrator, so as to correct that portion of time.
With this prior art, however, since an analog circuit including an integrator and the like is used, a lamp voltage of the integrator changes due to a change with time and a temperature change, which disadvantageously results in an error.